Demand for data services of higher speed and larger capacity is increasing as mobile terminals such as mobile phones become widespread and as multimedia expands. Especially, the orthogonal frequency division multiplexing (OFDM) scheme is considered to be a promising access scheme because demand for higher speed and larger capacity in the downlink is strong, and because efficient use of wide frequency bands is desired.
In the OFDMA, band is divided into chunks called resource blocks (RB) so as to frequency-multiplex a plurality of users. As assignment/transmission schemes for resource blocks, two schemes which are a localized RB scheme and a distributed RB scheme are defined (refer to non-patent document 1, for example).
In the localized RB scheme, contiguous bands are preferentially assigned to users in good channel state locally on a frequency axis. This scheme is advantageous for communication performed by a user of small mobility and is advantageous for high-quality and high-capacity data transmission and the like.
In the distributed RB scheme, a downlink signal is generated and transmitted by distributing subdivided frequency components over a wideband. According to this scheme, frequency diversity can be expected, so that this scheme is advantageous for data transmission by a user of large mobility, and for periodical transmission of small-sized data like voice packets (VoIP).
As shown in FIG. 1, in both of the localized RB scheme and the distributed RB scheme, each resource block assigned by the base station (cell) is specified by a resource block number (RB index). In the example shown in FIG. 1, in the localized RB scheme, if it is specified that a resource block of the RB number 2 is assigned, it is uniquely specified that resources of a physical resource block number 2 are actually used. When the base station specifies that a RB number 2 is assigned in the distributed RB scheme, it is uniquely specified that the left half of the physical resource block number 2 and the left half of the physical resource block number 8 are used. A relative resource block number assigned by the base station may be called “virtual resource block number” in a sense of distinguishing from the actual physical resource block number.
In addition, as shown in FIG. 2, it is proposed to allow coexistence of both of the localized RB scheme and the distributed RB scheme according to situations of users (refer to non-patent document 2, for example). When assignment and transmission of the distributed RB scheme become necessary for a user (for example, when starting high-speed movement), a part of localized RBs assigned by the base station is replaced with distributed RBs. Assuming that the number of resource blocks replaced by the distributed RBs is NDRB, positions used for distributed transmission are determined by a division number irrespective of NDRB. More particularly, a k-th block and a (k+6)-th block form a pair, and the pair is not changed irrespective of NDRB.
In the conventional method, when performing distributed transmission, the number (division number) of blocks into which one physical resource block is divided is determined in a fixed manner for each cell. The user apparatus recognizes mapping relationship between resource block numbers assigned by the base station in the distributed transmission and actual physical resource block positions, by using a broadcast channel and the like. In each user apparatus, after receiving, from the base station, a notification that the user apparatus is a target of distributed transmission in the current TTI, the user apparatus can receive, demodulate and decode a data channel at corresponding physical resource block positions based on the assigned virtual resource block numbers and the division number which is determined in a fixed manner.
[Non-patent document 1] 3GPP, R1-062089, NTT DoCoMo, et al. “Comparison between RB-level and Sub-carrier-level Distributed Transmission for Shared Data Channel in E-UTRA Downlink”.
[Non-patent document 2] 3GPP TSG RAN WG1 #49, Kobe, Japan, May 7-11, 2007, R1-072431, NTT DoCoMo, et al.